Discovery of molecular sieves containing octahedral framework chains represents an important new branch of molecular sieve science. Reference is made to U.S. Pat. No. 4,853,202 and U.S. Pat. No. 4,938,939 (Kuznicki et al).
ETS-4 described in U.S. Pat. No. 4,938,939, the entire disclosure of which is herein incorporated by reference, is a small-pored titano-silicate molecular sieve containing such chains. However, ETS-4 is characterized by poor thermal stability in the predominantly sodium exchange form in which it is typically synthesized, generally losing substantial structure and porosity near its dehydration temperature of approximately 200.degree. C. However, it is known, as described in U.S. Pat. No. 4,938,939 that ETS-4 in certain cation forms such as rare earth has a higher degree of thermal stability, at least 400.degree. C. or higher.
Water must generally be removed from a molecular sieve zeolite before it can be effectively employed as a sorbent. It is obvious that a dehydrated sieve will have limited utility as a sorbent unless it is stable at and beyond the temperatures at which it is dehydrated.
It has now been discovered that barium-exchanged ETS-4 not only has a high degree of thermal stability, but can be effectively used to separate nitrogen from a mixture of the same with methane.